Cavitation/fracture transition of soft materials

A defect in soft materials expands rapidly under a critical hydrostatic tension, causing cavitation or fracture. The mechanical properties of the material and the size of the defect have decisive influence on the failure mechanism. As different modes of material failure, the transition between cavitation and fracture is still elusive. Combining the Griffith's fracture criterion and finite deformation theory, we hereby obtained the critical initial defect size of cavitation/fracture transition. In the experiments, a cavitation rheology device was built to measure the failure mode of polyacrylamide hydrogels by inserting needles with various sizes. By observing the surface roughness and measuring critical expansion pressure of the bubble, we verified that the transition size is controlled by fractocohesive length Γ/Wf, which can be orders of magnitude smaller than elasto-adhesive length Γ/E. The present work reveals the transition mechanism between cavitation and fracture, quantifies the transition size, and provides a promising route to predict the failure behaviors of highly stretchable materials.